The present invention relates to an apparatus for lighting fluorescent lamp, particularly to a bulb-type fluorescent lamp, that is, a fluorescent lamp having a shape of electric bulb.
In recent years, in view of energy conservation and the like, bulb-type fluorescent lamps have been used instead of incandescent lamps. In a conventional bulb-type fluorescent lamp, a light-emitting tube, a starter and a stabilizer are integrated and accommodated in the screw base portion thereof, making the base portion large and heavy.
FIG. 47 is a circuit diagram of a conventional bulb-type fluorescent lamp. The circuit configuration of the bulb-type fluorescent lamp will be described below referring to FIG. 47.
An AC power source 101 is connected to the AC input terminals of a full-wave rectifier 104 via a filter circuit comprising an inductor 103 and a capacitor 102. A smoothing capacitor 105 is connected across the DC output terminals of the full-wave rectifier 104. To the smoothing capacitor 105, two switching devices 111 and 112 are connected in a half-bridge configuration. A transformer 114 for generating a resonance voltage has inductors 115, 116 and 117. One of the terminals of the inductor 115 of the transformer 114 is connected to the connection point (hereinafter simply referred to as the connection point between the switching devices) of the first switching devices 111 and the second switching device 112. A starting resistor 200 and a capacitor 201 are connected in parallel between the connection point between the switching devices and the smoothing capacitor 105. The parallel arrangement of a capacitor 204 and zener diodes 206 and 207 is connected between the gate terminal of the first switching device 111 and the connection point between the switching devices. The cathodes of the two zener diodes 206 and 207 are connected to each other in series. An inductor 202 is connected between the other terminal of the inductor 115 of the transformer 114 and the gate terminal of the first switching device 111.
An inductor 203 is connected between one of the terminals of the inductor 116 of the transformer 114 and the gate terminal of the second switching device 112. In addition, a smoothing capacitor 205 is connected between the other terminal of the inductor 116 and the gate terminal of the second switching device 112. Furthermore, two zener diodes 208 and 209 are directly connected between the other terminal of the inductor 116 and the gate terminal of the second switching terminal 112 in parallel with the smoothing capacitor 205. The cathodes of these two zener diodes 208 and 209 are connected to each other. A resistor 210 is connected between the connection point of the two zener diodes 208 and 209 and the other terminal of the second switching device 112. Moreover, the other terminal of the second switching terminal 112 is connected to the smoothing capacitor 205 via a capacitor 213.
One of the terminals of the inductor 117 of the transformer 114 is connected to the connection point between the switching devices, and a pair of filament terminals in a light-emitting tube 135 and a capacitor 134 are connected in series between the other terminal of this inductor 117 and a capacitor 133.
Next, the operation of the conventional bulb-type fluorescent lamp configured as described above will be described.
The starter of the conventional bulb-type fluorescent lamp shown in FIG. 47 includes the two switching devices 111 and 112, the inductor 117 used as the secondary winding of the transformer 114 and the capacitors 133 and 134 connected to the light-emitting tube 135. The two switching devices 111 and 112 turn on and off alternatively at high speed, thereby converting the DC voltage across the smoothing capacitor 105 into a high-frequency signal. As a result, the light-emitting tube 135 is set in a lighting state by the high-frequency signal. The capacitor 134 inserted and connected across the pair of filament electrodes of the light-emitting tube 135 forms the current path of the preheating current for filaments of the light-emitting tube 135, and is also used as a resonance capacitor in combination with the inductor 117.
The capacitor 133 is a coupling capacitor used to cut DC components in the power source. To alternatively switch the two switching devices 111 and 112, the inductors 115 and 116 of the transformer 114 detect the timing of on/off operation, and the inductors 202 and 203 carry out driving.
The starting resistor 200 turns on the first switching device 111 at the time of power-on to start the starter. In this way, until the starter is started by power-on and the light-emitting tube 135 is lit, resonance is caused at the inductor 117 and the capacitor 134 constituting a resonance circuit by the two switching devices 111 and 112, thereby generating a high voltage and lighting the light-emitting tube 135.
After the light-emitting tube 135 is lit, the impedance across the light-emitting tube 135 becomes low. As a result, the resonance capacitor 134 becomes nearly short-circuited. For this reason, self-oscillation occurs at the low resonance frequency determined by the capacitor 133 and the inductor 117, whereby the light-emitting tube 135 can continue high-frequency lighting operation at high efficiency.
However, in the above-mentioned conventional bulb-type fluorescent lamp, a high voltage is generated for lighting at the resonance frequency determined by the inductor 117 and the capacitor 134, immediately when and after the power is turned on. Therefore, at the time of lighting, the above-mentioned lighting operation is carried out while the external tube of the light-emitting tube is still cool, without sufficiently heating the filaments. Therefore, stress is applied to the filaments of the light-emitting tube, thereby causing a problem of shortening the service life of the light-emitting tube.
Furthermore, in the conventional bulb-type fluorescent lamp, the preheating time for the filaments cannot be taken sufficiently, thereby causing a problem of making the luminous flux small because the temperature of the external tube is low immediately after lighting, and making the luminous flux larger as the temperature of the external tube rises.